U.S. Pat. No. 6,276,953 B1 describes a plug of the type in which a sparking contact normally provided in an ignition coil is integrated into the plug. A shorting contact is broken so that current cannot flow in the shorting contact by pushing in a position assurance member, which is fitted at a side of the plug. When the plug is not inserted, the position assurance member is in an initial position in which current can flow in the shorting contact. Pushing the position assurance member into the plug and hence breaking the shorting contact so that current can not flow in the shorting contact is not possible in the initial position.
It is only by inserting the plug into the socket that a flexural member, which has prevented the position assurance member from being pushed in, is removed and that the shorting contact can be broken so that current cannot flow in the shorting contact. At the same time, an arm of the position assurance member fixes the plug in the socket and prevents the plug from being removed from the socket. Moving the shorting contact into the plug increases the complexity of the plug and is, moreover, not equally suitable for all customary sockets. It also impairs handling of the plug.
In the case of a plug known from EP 0 600 418 B1, a shorting contact located in a socket of an airbag is broken when the plug is inserted into the socket. This takes place when a front end of a plastic casing of the plug is pushed between a contact pin and a contact spring of the socket. When the plug is plugged in, the plug is initially inserted into the socket until the socket meets resistance. The plug is then pushed with force past the resistance until the plug breaks the shorting contact so that current cannot flow in the shorting contact and engages with several projections on the socket. As it engages, the plug is fixed on the socket. Since fixing and breaking of the shorting contact takes place simultaneously, measurements, for example, for testing or checking purposes are not possible once the plug is inserted. This is a marked disadvantage.